When discharging from larger storage silo cells there are three ranges of problems which must be taken into consideration particularly: the reliable discharging of the product, the metering, and the elimination of any disturbance of the flow behavior inside the silo. Throttle cross-sections, for example, with or without adjustable slides, corresponding approximately to the outlet design of liquid containing tanks, are sufficient for free-flowing and fluid goods.
Farinaceous goods are a special case, since the flour flows down and out without help in the manner of a thick-flowing mass when the silo-outlet cross-sections are correctly designed. Should any disturbance occur in the free outlet area or should a favorable flow-out zone occur, this usually results in a corresponding one-sided emptying of the entire silo volume due to the supporting forces of the bulk goods particles. The silo is emptied in a chimney-like manner via the preferred flow-off cross-section. This results in longer storage times for the remaining stored goods and, in foodstuffs, is often the reason for a reduction in quality of the goods and can lead in extreme cases to the decay of the foodstuff.
Discharge cylinders have been used for many decades for the metered discharging of flour from large storage boxes. The very widespread use of discharge cylinders during the past decade is proof that the three ranges of problems formulated in the beginning could be solved with them, at least in principle. The discharge cylinders can be manufactured in considerable lengths. Usually, it was not necessary to taper the silo outlet area in the longitudinal direction of the discharge cylinders. Disturbances or the danger of a one-sided flowing out, respectively, have been countered in recent years by installing unloading bodies, unloading saddles, etc. inside the silo.
An embodiment example for such a solution is shown in the GB-PS No. 788 797. In this case, two discharge cylinders or a double-cylinder pair, respectively, are installed inside a discharge hopper which is fastenable at a lower part of the silo. The silo body comprises a conically reduced outlet, an unloading saddle being arranged in its upper part. The unloading saddle, which is arranged in the middle, above the discharge cylinders, forces the product onto two lateral flow-out zones. It is interesting to note in this solution that the conically reduced outlet in the discharge hopper is continued until slightly above the two discharge cylinders in a stepwise manner. However, the concrete solution, as shown in the GB-PS No. 788 797, would not be suitable for the discharge of flour from storage silos, since flour can often adopt the flow behavior of water, because the flour is fluidizable to a considerable extent. A known device for discharging flour, from a silo cell is described in the DE-OS No. 1 456 692, but comprises only one discharge cylinder. The lower part of the silo was also given a particular shape in this instance, rounded, inclined side walls and a flow body over the inclined surfaces of the silo outlet. The discharge cylinder completely closes the lower silo outlet opening, so that the quantity of product discharged in each instance is determined by means of the contents of the chambers formed at the circumference of the discharge cylinders, as well as by the rate of rotation of the discharge cylinders. A one-sided discharge from the lower silo discharge area, and accordingly a one-sided downward movement in the silo, can be prevented by means of regularly reversing the direction of rotation. The fundamental disadvantage of the solution according to DE-OS No. 1 456 692 consists in the particular design of the lower portion of the silo required by the teaching according to the invention. This may be a good solution in individual cases, but is not technically applicable in the majority of cases. The silo bodies are often constructed in situ by available specialists. Inferior execution of this work must be taken into account frequently, precisely in those areas where the technical training is not as good. This is why the best inventions frequently fail, half of them being realized in a manufacturing plant under the full supervision of the inventor, while the other half are realized in foreign countries without his supervision. In this way, the solution, according to the invention, is simply not realized completely.